Ductile binary chromium alloy



United States Patent O 3,239,335 DUCTILE BINARY CHROMIUM ALLOY @scar Norman Carlson, Frederick A. Schmidt, and Le Vaughn L. Sherwood, Ames, Iowa, assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Oct. 11, 1963, Ser. No. 315,727 4 Claims. (Cl. *7S- 176) The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

This invention deals with ductile chromium-base metals and the process of making them.

Pure chromium metal, on account of its high melting point, high-temperature oxidation resistance, and hightemperature strength is used for construction equipment that is to be employed at elevated temperatures. It is very desirable, on account of these characteristics, to use chromium as the material of construction for space ships. However, brittleness makes chromium unsuitable for this purpose; this problem is especially encountered at the point of re-entry into space.

lt is an object of this invention to provide a chromium material of great ductility which also has the `above-mentioned high-temperature characteristics.

It was found that by the addition of from 0.1 to 0.5% by weight of a metal which has about the same atomic diameter as chromium and which forms a solid solution with chromium, the temperature at which the ductile chromium phase becomes brittle, the ductile-brittle transition temperature, is substantially reduced. It was also found that the best results are obtained with metals whose atomic diameter is the same as that of chromium, or longer than it by up to 15%, and that with metals having an atomic diameter greater than that of chromium by more than 15% the ductile-brittle transition temperature is increased.

The maximum decrease of the ductile-brittle transition temperature is obtained with metals whose diameter is greater than that of chromium by from 2 to 10%. The metals with which the desired result has been accomplished are: manganese; rhenium; technetium; platinum; ruthenium; osmium; rhodium; iridium; palladium; molybdenum; silver; gold; aluminum; copper; tantalum; niobium; vanadium; and tungsten.

Iodide chromium was used for the preparation of the binary alloys of this invention. This chromium was of extremely high purity and contained impurities in a total of less than 100 parts per million; they were mainly o carbon, nitrogen, oxygen, aluminum, iron and silicon. The additive metals used also were of the highest purity available.

Weighed quantities of -chromium and of the alloying metals were arc-melted together in a noneonsumable arc furnace in an argon atmosphere; the metals were thereby cast into buttons of about 80 grams. The buttons, after cooling, were checked for homogeneity; they were usually found to have a rather coarse grain structure which varied between 0.25 and 15 grains/mm2; the predominant grain size was between 0.25 and 0.6 grain/mm?.

For testing the ductility of the various alloys, test specimens were directly eut from these buttons. For this purpose, the buttons were cut into sections on a silicon -carbide cut-off wheel, and the sections were then ground on an alundum-surface grinding wheel into flat specimens 1" X 0.25" x 0.045". These specimens were finally electropolished in an orthophosphoric acid solution to a thickness of 0.040i-001 inch.

The ductile-brittle transition temperature was determined on a three-point bend test apparatus as it is described in an article by A. H. Sully et al. in J. Inst. Metals 81 (1952-53), 587. The specimens were supported over a span of 15716 and bent by a plunger rod whose end had a radius of 1/16; the plunger moved at a constant rate of 0.050 iti/min.

5 The deilection of the sample was measured by means of a dial gauge in contact with the plunger. Elevated test temperatures were maintained by means of an electrically heated resistance furnace while sub-ambient temperatures were attained by flowing liquid nitrogen through an insulated copper jacket surrounding the support block.

Bend tests were carried out at intervals of C. or less and the ductile-brittle transition temperature was determined from curves plotted from deection at fracture (ordinate) and test temperature (abscissa). S-

l5 shaped curves with practically horizontal branches at start and end and practically vertical sections therebetween were obtained. The transition temperature was taken as midpoint of the vertical transition range section of the curve corresponding to a deection of 150 mils. A 250- mil deflection was equivalent to a bend angle of 90, the

approximate limit of the apparatus.

The transition temperature of unalloyed arc-melted chromium was determined to be at -45i5 C. In the table which follows the ductile-brittle transition temperatures obtained by the bend ductility tests are compiled for the `binary chromium alloys tested. It is obvious from said table that the rst group of metals when added `in a quantity of 0.1% by weight, lowers the ductile-brittle n transition temperature and in many cases also reduces 00 this temperature when added in a quantity of 0.5% by weight (exceptions: Al, Cu, Au, Nb, Pd, Rh, Ag, W and V). In almost all instances of the first group of metals, the percentages of 1.5 and 3.0% proved unsatisfactory,

because then the ductile-brittle transition temperature was increased rather than decreased. A percentage of 0.1

seems to be the optimal quantity.

Duetile-Brittle Transition Temperature, C. (5:10 C.) A

Alloying Element Nominal Composition, in

Wt. Percent Aluminum -35 Copper.. -20 o1d so 40 Iridium. -85 Niobiu m -55 20 Manganese. -GO

FO Molybdenum-- -65 -65 Osmiuin... -60 Palladium. -60 15 P1stinum so 80 Rheniunm. -35 Rhodium -75 -55 Ruthen1um -85 -75 55 Silver -55 10 Tantalum... -55 -55 Tungsten.- -55 -10 Vanadium. -50 -30 Cobalt -45 25 Hafnium-.. 45 40D Iron 30 35 Nickel-. 40 200 60 Tm -25 135 Titanium.. -35 250 Uranium l5 140 Zirconium. 235 400 Cerium. 20 35 Dysprosium. 60 Gadolinium.. 40 70 Lanthanum. 15 35 65 Neodymium 15 10 Praseodymium. 10

Seandium- 50 Thoriurn... 65 50 Yttrium so 65 The metals of the second group shown in the table, it will be obvious, are unsuitable for the purpose of this invention, since they raise, rather than lower, the ductilebrittle point in all instances; this is true for all proportions shown, the increases being greater with increasing quantities of the additive metal. Likewise, the metals of the third group increased the ductile-brittle transition temperature, although there, increasing quantities of the alloying metal have a less pronounced effect on the ductile-brittle transition temperature than lesser quantities. It is obvious though that the metals of the rst group only accomplish the object of this invention and that the quantity ot' these additive metals is critical.

In the accompanying drawing, the transition temperatures of the various binary alloys tested (content of alloyed metal 0.1 atomic percent) are plotted against the atomic diameters of the additive, alloying, metal. It will be obvious from this drawing that the metals having an atomic diameter up to about 2.88 (which is about 15% greater than the diameter of 2.5 of chromium) have a decreasing effect on the ductile-brittle transition ternperature. The highest decrease of the transition temperature is accomplished with metals whose atomic diameter is from 2 to 10% greater than that of chromium.

An analogous diagram for the binary chromium alloys containing 0.3 atomic percent of the alloying .metal showed similar results; however, in that case fewer metals had a reducing effect on the ductile-brittle transition temperature.

It was determined metallographically that all of the metals which show a reducing effect on the transition temperature form a solid solution with chromium when added in the quantities shown.

It will be understood that the invention is not to be limited to the details disclosed herein but that it may be modified within the scope of the appended claims.

What is claimed is:

1. A ductie binary chromium alloy consisting essentially of from 0.1 to 0.5 percent by weight of a metal whose atomic diameter is longer than that of chromium by up to 15% and which forms a solid solution with chromium in said quantity range.

2. The ductile binary chromium alloy of claim 1 wherein the diameter of said metal is by 2 to 10% longer than that of chromium.

3. The ductile binary chromium alloy of claim 1 wherein said metal is selected from the group consisting of manganese, rhenium, technetium, platinum, ruthenium, osmium, rhodium, iridium, palladium, molybdenum, silver, gold, aluminum, copper, tantalum, niobium, vanadium and tungsten.

4. The ductile binary chromium alloy of claim 3 wherein the content of said alloying metal is about 0.1% by weight.

Hansen: Constitution of Binary Alloys, McGraw-Hill Book Company, Inc., New York, 1958, pages 523, 524, 535, 537, 541, 548, 550, 552, 555, 556, 563, 570.

DAVID L. RECK, Primary Examiner.

R. O. DEAN, Assistant Examiner. 

1. A DUCTILE BINARY CHROMIUM ALLOY CONSISTING ESSENTIALLY OF FROM 0.1 TO 0.5 PERCENT BY WEIGHT OF A METAL WHOSE ATOMIC DIAMETER IS LONGER THAN THAT OF CHROMIUM BY UP TO 15% AND WHICH FORMS A SOLID SOLUTION WITH CHROMIUM IN SAID QUANTITY RANGE. 